Boston and Maine No. 3713, also known as the "Constitution", is the sole survivor of the "P-4a" class 4-6-2 "Heavy Pacific" type steam locomotives. It was built by the Lima Locomotive Works for the Boston and Maine Railroad in December 1934. As of 2022, the No. 3713 locomotive is currently being restored to operating condition at the Steamtown National Historic Site in Scranton, Pennsylvania as part of their operating fleet for use on excursion trains. It was the focus of Project 3713, a partnership between the National Park Service and the Lackawanna & Wyoming Valley Railway Historical Society.